This proposal requests the funds to purchase a FACSVantage SE flow cytometer for the Lombardi Cancer Center (LCC) Flow Cytometry/Cell Sorting Shared Resource. This instrument is intended as a replacement and upgrade for an existing and outdated FACStar Plus purchased in 1988. The Resource maintains the only cytometers accessible to researchers on the campus, the only instrument with tunable lasers and exchangeable emission filters as well as the only fluorescence activated cell sorters at Georgetown University (GU). The current cytometer, the FACStar Plus, has been out of production since 1992 and it is becoming more difficult to obtain repair parts. The proposed new cytometer will allow more complex multicolor analyses required for ongoing NIH funded projects along with great improvements in cell sorting capabilities. The TurboSort feature will allow investigators to sort out large numbers of cells or to isolate sufficient quantities of rare event populations, which are now not feasible to sort due to time constraints. The QuadraSort capability will be valuable in sorting multiple populations, particularly from samples with limited cell numbers. An additional feature will allow for the sorting of nonrectangular populations. Of the 23 major users, 8 currently have projects which require capabilities not available on the present instrumentation. Other projects would be enhanced by these features. More than 40 PIs would greatly benefit from the availability of a reliable state-of-the-art cytometer. The Resource is heavily utilized by investigators from 11 departments. In 2001, 43 investigators utilized the facility for more than 750 experiments. Currently, there are more than 29 investigators with peer-reviewed NIH funded projects utilizing the facility along with 5 investigators with peer reviewed funded projects from other funding sources. The Resource, established in 1988, is supported by a combination of Cancer Center funding, NCI CCSG grant support, and user fees. The Resource is headed by Dr. Karen Creswell, who has 12 years of experience in flow cytometry, and who will serve as the primary instrument operator. An advisory committee oversees access, fees, policies, and makes recommendations for future growth. The LCC is committed to support this Resource to ensure continued upkeep, excellent service and wide access to the GU community.